Hi Everyone,
I'm new to the forum and look forward to seeking advice and giving it too, If I can.

I have a 1994 with a 3.4 that I bought NEW back in some other time. It has 325,000 miles and has never had a wrench on the "engine-proper," transmission, or rear axle.
We still drive it daily and it has become my 16 y/o daughter's first car. It's a reliable car and other than oil and transmission leaks, and the non-working keyless entry, everything works.

For a couple of years, it has consistently had a problem and I recently retired so now I have time to chase it down and fix it. Your help would be appreciated. I had to have the fuel pump replaced in the late 1990's and it was done at the Chevy dealer under a promo where parts AND labor had a LIFETIME WARRANTY for the ORIGINAL OWNER. I had it replaced again in about 2018. My problem has existed ever since. The Here's the specifics.

* When getting gas, removing the cap reveals extremely high pressure in the tank, probably 12-16 pounds (estimated)
* On the first start of the day, it takes 3 or 4 burst of the starter, about seconds each, and it almost starts on the next-to-last burst but does start on the next one.
* After a long parked period of 6+ hours, that repeats. On short parked periods, it starts fine.
* Engine runs smooth, plugs look good, no hesitation, no fuel smell under hood or under car. No dripping.
* Recently changed fuel filter, plugs, and fuel pressure diaphragm, and installed a new catalytic converter with no effect on problems.
* Inside tailpipe has always been black and sooty, even at 10,000 miles.
* Since new and after first fuel pump replacement, average fuel consumption was in the 26 to 29 MPG range.
* Since second fuel pump install, average fuel consumption has been about 17 MPG. VERY SIGNIFICANT CHANGE !

1.3 GALLONS PER DRIVING HOUR ARE VANISHING. I worry that the crankcase oil reservoir is acting as an evaporation mechanism for that fuel and if so, Meg's engine is housing explosive vapor above the oil, just waiting for an ignition source. On the dipstick, the oil looks normal and does not smell "gassy."

Any new ideas? I have had the $600 set of factory shop manuals since I bought the car and they are my first source for troubleshooting info. I have read everything and exhausted my brain.

Any ideas are appreciated.

Bryan Cobb

 

sure sounds like fuel pump install did something. read up on the evap system. test the fuel pressure, at no start and at running temp. low or high fuel pressure can cause engine to run rich. with that many miles and years I would have the injectors cleaned and flow tested. I am wondering if they crossed one of the evap hoses or damaged it some way. you should smell gas in the exhaust while running. gas has to be going some place. my lt1 runs rich while warming up and its not really gas smell but its not fun to breath.

 

I have some homework to do now.

Bryan

 

The 1994 Camaro with 3.4 V-6 was going to become our daughter's college-commuter to her school, 500 miles away. We decided it was time for the rebuild at almost 325,000 miles.
My highly skilled mechanic was the Service Department Manager at the local Chevy dealer in the 1990's and now works out of his own shop.

I paid him a little over $7000 to rebuild the engine. He prefers to personally rebuild and use his preferred machine shop, instead of getting a "Jasper" reman, or similar. After the rebuild,
It's running well but only gets 13-14 MPG! When the car was new, it got 28-29. Every component of the fuel delivery system is new. It has black smoke during hard acceleration and after 150
Interstate miles, it needs gas and heavy soot is in the exhaust outlet. After an oil change, the new oil turns jet-black after only 700-800 miles.

The first two oil fills after the rebuild had Zinc added for cam/lifter break-in. My mechanic has a theory that excess raw, unburned liquid gasoline in the cylinders is rinsing the oil off the cylinder walls
and out of the rings, compromising the seal and leaking explosive/hot gasses into the crankcase where it sometimes ignites. No evidence of liquid gas making it all the way to the tailpipe. When we remove the gas cap to refuel, there's no pressure escaping like there was back when the car was new.

Any ideas? He's trying to get his hands on a 1990's-era diagnostic "tech-tool" from a Chevy dealer to diagnose the issue. Here's more specifics. New catalytic converter. Mass Airflow Sensor not replaced. ECM not replaced. New crank position, cam position, and other engine sensors. New air filter, plugs, wires. New fuel pressure regulator and injectors. Evap hoses new but may not be routed correctly.

Any advice from someone would be appreciated.

Bryan Cobb

 

What are the o2's reporting? Are you even in closed loop operations?

There are a lot of things that can cause rich condition at idle. Under load this is shorter list. If the MAP, MAF and Air temp sensors or fuel pressure (assume all plugs cylinders are effected) can all cause rich issues but in closed loop the O2 sensors should see this and set a check engine light. It should even flash if its as rich as you indicate. Was something done to by pass the check engine light that should be triggered due to no Cat?

There are so many inputs that the computer is capable of reducing the fuel going into the motor. If it is out of acceptable fuel range the PCM should take the system offline and run on pre define numbers using minimum data from the sensors(AKA OPEN LOOP). I most cases an off line or open loop car does not run that bad. For it to run as poorly as you are saying that would mean the the is a major problem with a main sensor.

How is the car for power?

 

Answers: Don't know if running in closed loop or open loop right now. Both O2 sensors are new as of rebuilt engine install. It had a new Catalytic Converter installed about a year ago.
No error codes are being throw, or if they are, it's not activating the check engine light. It seems to be running ok, power ok except for smoke. Very stock and no bypassing systems.

Bryan

 

My bad I miss read the post, Scan tool should tell you what is going on assuming the tech knows what he is looking as. This is not some little fuel issue. Don't drive it! If black smoke is getting passed a new CAT then the motor is very rich and the cat is trying to burn it. That means the cat is about a 1000 degs. I have seen them glowing red. Any leaves blowing around can become a problem. An issue that bad should have the check engine light blinking. There is a good chance you will need new O2s once you figure this out. Also a oil change would be a good idea due to gas in the oil.

I was a master tech in the 80's into the 90's no way would I have let a car I just charged 7K to work on leave blowing black smoke. I would rather build my own engines also but they teach you in class there is a point when the cost becomes the ruling factor. 30 years and 325K miles is beyond the design limits of every system in that car. I would not be surprised if just moving the wires around broke a bunch of them.

 

OK folks. The Camaro has only had 70 miles driven by me in the past year. It has sat under the carport the rest of the time and the kid took the Tahoe to college. The Tahoe just passed 400,000 miles and still doing well.

Before the Camaro was parked, my engine builder (A local Chevy dealer mechanic from the 90's and high school friend) was able to eliminate the hard starting. I forget what the problem was but it seems like it was
a puzzle of erroneous data sent to the ECM. I had a spare ECM and both had the same hard-start issue.

When Grady rebuilt the engine, every electronic device on the engine was replaced new EXCEPT THE SIX FUEL INJECTORS, as was the fuel pressure regulator diaphragm. When the car was new, it consistently got 28.? MPG on road trips. It stayed relatively close to that until we got a new Tahoe in May 2006 (2007 model year). The Camaro was rarely driven between 2006 and 2019 when the kid turned 15 and started learning to drive. At that time, fuel efficiency had crashed to 16 MPG!!!. She drove it in that condition from 2019 till Grady rebuilt the engine in 2021.

We didn't learn till later, that one cylinder was being flooded with so much liquid fuel that it never atomized and got a chance to be burned. After the engine rebuild, that continued. Grady reinstalled the original fuel injectors that came on the car in 1994. I don't know why. I guess he had confidence they were working right. At Grady's first oil change after the rebuild, at only 2000 miles, the oil was black and smelled burnt. We discussed it and attributed it to the zinc we had added for camshaft conditioning.

The kid took the car 500 miles away to college , all the time the newly-rebuilt engine was turning the oil black quickly and only getting 16 MPG. She had a school break and drove it home. I had her take the Tahoe back. Since, Grady and I, have investigated and convinced ourselves that the old fuel injectors are the culprit. We feel, in the 13 years the car sat undriven, from 2006-2019, one or more of the fuel injectors developed a "stuck ON" condition which flooded the cylinder(s), flushed the oil out of the rings, and allowed raw fuel into the oil in the crankcase. It's probable that hot oil evaporated some of the fuel into the air space in the crankcase. Sometimes on long drives, we'd pull into a gas station and turn off the car. After filling up and getting a snack, we'd return to the car and when the engine was started, the fumes in the crankcase would explode and the engine would shudder for a few minutes as it attempted to burn excess gas in at least one cylinder.

I am about to finally replace the six fuel injectors, and expect all the problems to go away. Since Grady does not have a 1990's-vintage TECH-TOOL, calibration data and tuning may not be something we can accomplish. I know, by being an aircraft owner, that best stoichiometric mixture on all cylinders can only be achieved if fuel injectors are accurately flow-matched. Then and only then, you can lean to slightly leaner than PEAK EXHAUST GAS TEMPERATURE. This saves a lot of money by conserving fuel without damaging the engine. GOOGLE "GAMI Fuel Injectors and running your engine lean of peak.". By the way, the fuel pump and filter are clean and fuel lines have been checked for the need for stents.

HERE'S A FEW QUESTIONS I HAVE ON HOW TO PROCEED:
1). I know the importance of flow-matching the injectors. What injectors would you buy? Bosch? GM OEM P/N 19244620?, ACCEL?
2) How can we read FLOW rate on each cylinder at 70MPH?
3). How can "dial-in" the injectors without av1990's TECH TOOL?
4) What's best method to lean until ZERO SOOT is in tailpipe and it's nice and gray.

Answers are appreciated,
Bryan Cobb

 

have the old injectors inspected by a injector shop like doctor injector. you will know then if that is the issue. it may be they just need to be cleaned and flow tested. if they are no good the injector shop may have some reman'd ones that are flow tested for good price. I like to send new ones in to be flow tested and matched.

 

Thank you,

Are they "out west?"